The following invention relates to a bearing guided labyrinth for use in electronic spindle motors having ball bearing rings.
Known electric spindle motors of the type used in disk drives conventionally use ball bearing assemblies to facilitate movement between a rotary member and a stationary member. Ball bearing assemblies generally include metallic or ceramic ball bearings which are positioned between an inner bearing ring and an outer bearing ring. Bearing rings may be either inner or outer rotators depending on whether the hub or shaft rotates. Inner rotators have an inner bearing ring that rotates, and outer rotators have an outer bearing ring that rotates. The ball bearings are preferably evenly spaced within the inner and outer bearing rings. The ball bearings are generally held in this evenly spaced position by teeth of a ball bearing cage (not shown).
Bearing lubricant fluid is used in bearing assemblies to encourage free movement of the ball bearings, the inner bearing ring, and the outer bearing ring. Conventionally, the lubricant is initially deposited on the teeth of the bearing cage. During use, however, the lubricant tends to migrate and eventually escapes the bearing ring. The lubricant that migrates and escapes the bearing ring often enters the interior of the motor or exits the motor completely.
One cause of lubricant migration is the rotation of the bearing assembly and centrifugal pull that causes the lubricant to be thrown from the bearing assembly. Although lubricant generally is not thrown from a bearing assembly at lower rotation speeds, higher rotation speeds tend to disperse or "sling out" lubricant. At particularly high speeds the lubrication is atomized.
Another cause of lubricant migration is airflow through the motor and bearing assemblies which tends to push lubricant, particularly atomized lubricant, out of the bearing assembly. Airflow also tends to carry particles and contaminants. Designers of motors try to reduce airflow to reduce or eliminate these problems. The use of bearing shields reduces the flow of air and contaminants through the bearing assembly and thereby partially inhibits the loss of lubricant from the bearing assembly.
Once the lubricant escapes the bearing assembly it enters the horizontal gap between the top surface of the ball bearing assembly and the bottom surface of the washer (or other enclosing apparatus). The lubricant then travels from the horizontal gap up through the vertical air gap between the inner surface of the washer and the smooth outer surface of the shaft. The lubricant then can escape the motor.
Using fluid labyrinths to prevent lubrication fluid from escaping a fluid bearing spindle motor is shown in U.S. Pat. No. 5,536,088 which is assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference. Fluid labyrinths found in such fluid bearing spindle motors are generally the winding path in which the lubrication fluid resides, at least part of which forms the fluid bearings. Fluid labyrinths are not used with ball bearing spindle motors because the lubrication fluid is not intended as a bearing but instead is used to facilitate rotation between the ball bearings and the inner and outer bearing rings. Accordingly, the lubrication fluid is not intended to enter the air gaps.
FIG. 1 shows a labyrinth seal system shown in U.S. patent application Ser. No. 08/712,615 which is assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference. The shown motor incorporates a labyrinth seal system that includes at least one rotating member (either a hub 26 or a shaft 28) that rotates in relation to another member (either the shaft 28 or the hub 26). The rotating member is separated from the other member by a ball bearing assembly 18 that has an inner bearing ring 22 and an outer bearing ring 24 separated by a plurality of ball bearings 20. A labyrinth seal washer 40 having an annular leg 42 positioned at least partially between the outer surface of the shaft 28 and the inner surface of the inner bearing ring 22.
None of the prior art has found a solution that completely prevents oil from migrating out of a motor.